FIG. 1 shows a thermally heavy-duty electrode known from the prior art, on the left before melting over the electrode coil, on the right after melting, in cross-section in each case, as used for example to achieve good maintenance with high-pressure discharge lamps. In this case high-purity tungsten is used both for the pin 12 and for the electrode coil 14, i.e. tungsten with additives, the concentration of which is less than or equal to 20 ppm. However, this results in the disadvantage of a low recrystallization temperature, as a result of which the electrodes very easily become brittle at higher temperatures, especially during operation of the lamp. Melting over an electrode coil in order to create a thermally compact mass 16 is already known from DE 1 170 542. Rejects resulting from the known brittleness are accepted, or are avoided by preventing impacts as much as possible during handling. Hence use for example as a car lamp is not possible with electrodes of this type.
FIG. 2 shows a further generic electrode known from the prior art, in which tungsten is used with microstructure-stablilizing additives, for example potassium, wherein the concentration of the additives both in the material used for the pin and the material used for the electrode coil is greater than or equal to 30 ppm. Although the brittleness is reduced, these additives have a negative impact on the service life of the lamp. Additionally, microstructure-stabilized electrode coils melt only with great difficulty, since the stabilizing addives result in the formation of cavities 18. At present such electrodes are used in applications with a high probability of impact, for example car lamps, and their service life restrictions are accepted.